The present invention relates to an ultrasonic cleaning apparatus, more specifically to a household ultrasonic cleaning apparatus for cleaning, for example, fabrics, textile products and the like and an ultrasonic cleaning method.
As a technologies for cleaning dirty textile products and the like by use of an ultrasonic oscillator, a control apparatus of a washing machine disclosed in Japanese Patent Laid-Open No. 11(1999)-104388 has been heretofore known. In the control apparatus of a washing machine disclosed in this gazette, a partial cleaning unit which is pressed against dirty portions of clothes and removes the stains is constituted by a piezoelectric element, and electrical signals are supplied to the piezoelectric element by amplifying an amplitude of an output signal of a controller by an amplitude amplifier. Power is supplied from a power supplier to the amplitude amplifier, and an operation state of the piezoelectric element is detected by a state detector. Then, the control apparatus controls a frequency of the output signal of the controller so that the piezoelectric element and the amplitude amplifier are synchronized with each other by an output of the state detector.
In the ultrasonic cleaning apparatus, an oscillator is dipped in cleaning liquid while dipping the subject to be cleaned in the cleaning liquid, and stains attached to the subject to be cleaned are removed by propagating ultrasonic waves generated in an ultrasonic oscillation circuit to the subject to be cleaned. In this ease, impedance of an oscillation circuit changes along with a change of a depth of the cleaning liquid. To be specific, when stationary wave are generated, a secondary output current of a coupling transformer provided between an oscillator and the oscillation circuit drops. Therefore, there has been a problem that an oscillation amplitude of the ultrasonic oscillator becomes small and a cleaning capability of the ultrasonic cleaning apparatus is lowered.
As a technology for solving this problem, there has been an ultrasonic cleaning machine disclosed in Japanese Patent Laid-Open 63(1988)-162086. In this ultrasonic cleaning machine, an oscillation amplitude of an oscillation circuit is detected, and impedance of a coupling transformer when viewed from primary windings is made to be small by automatically controlling the coupling transformer by uses of the detected oscillation amplitude as a control quantity so that the number of secondary windings is large. Thus, a constant oscillation amplitude is obtained regardless of a change in a liquid depth and a level of a load.
Furthermore, in xe2x80x9cUltrasonic Technologyxe2x80x9d published by Corona Co. Ltd., p. 67, a principle for driving an oscillator by use of a phase synchronizing oscillator is described. In the phase synchronizing oscillator, current flowing through an oscillator or a voltage across the oscillator are detected, and a frequency of a voltage control oscillation circuit is controlled so that a phase difference between the detected voltage and the detected current approaches a predetermined level. Thus, the oscillator is driven while following a resonance frequency or a proper frequency near the resonance frequency.
However, in the control apparatus of the cleaning machine described in Japanese Patent Laid-Open No. 11(1999)-104388, a voltage/current characteristic makes a unique change for a frequency in case of an electrostriction piezoelectric element, so that an effective control cannot be performed.
In the ultrasonic cleaning machine disclosed in Japanese Patent Laid-Open No. 63(1988)-162086, since the number of the secondary windings of the coupling transformer is made to be large so that the constant oscillation amplitude is obtained regardless of the change of the liquid depth and the level of the load, the coupling transformer is large-sized and hence the cleaning machine itself is large-sized.
In the oscillator drive using the phase synchronizing oscillator, it is absolutely impossible to cope with phase jumping due to a stationary wave occured in cleaning liquid when the phase synchronizing oscillator is used. Moreover, since the phase of the voltage and the phase of the current are made to be coincident with each other irrespective of the change of the load, a large amount of waste is produced in low power consumption.
Furthermore, in the oscillator drive using the phase synchronizing oscillator, a resonance frequency rapidly changes owing to a change of a load when the oscillator is used in cleaning liquid, and hence the resonance point cannot be discriminated from an anti-resonance point. Thus, the oscillator may be uncontrollable. This is because the current and the voltage show an identical phase in the resonance point and the anti-resonance point and the resonance point and the anti-resonance point cannot be discriminated from each other by the phase synchronizing control.
In order to enhance a drivability of the cleaning apparatus when cleaning is performed temporarily, a more compact-sized cleaning apparatus is required. However, when an output of the cleaning apparatus is made to be small, the output is apt to be influenced by a load. On the other hand, the applied load always changes depending on conditions of clothes and the like. In such a compact-sized cleaning apparatus, the possible uncontrollability increases. Therefore, a stable ultrasonic oscillation circuit and an oscillation element showing excellent cleaning effects are necessary in the foregoing various situations.
An object of the present invention is to provide an ultrasonic cleaning apparatus capable of exhibiting excellent cleaning effects with less power and cleaning dirty clothes easily.
A first aspect of the present invention is an ultrasonic cleaning apparatus which cleans a subject to be cleaned by oscillations generated by an ultrasonic oscillator, the ultrasonic cleaning apparatus comprising: a power amplifier for amplifying an amplitude of a signal to supply the amplified signal to the ultrasonic oscillator; a phase comparator for determining a difference between a phase of a current flowing through the ultrasonic oscillator and a phase of a voltage applied to the ultrasonic oscillator to generate a voltage in accordance with the phase difference; and a voltage control oscillation device for generating a frequency of the signal in accordance with the voltage generated by the phase comparator and for controlling the frequency so that the phase difference is held within a predetermined phase range, wherein the power supplied to the ultrasonic oscillator is set to a range of 1W to 10W
According to the first aspect of the present invention, the power supplied to the ultrasonic oscillator is set to the range of 1W to 10W, and the phase comparator generates the voltage in accordance with the phase difference between the current and the voltage. The voltage control oscillation device generates the frequency of the signal in accordance with the generated voltage, and controls the frequency so that the phase difference is held within the predetermined phase range. Therefore, effective power supplied to the ultrasonic oscillator can be increased, and influences of the phase shift due to the change of the load can be lessened.
In addition to the first aspect of the present invention, a second aspect of the present invention is characterized in that the voltage control oscillation device holds the phase difference to a range within xc2x130xc2x0.
According to the second aspect of the present invention, the effects of the first aspect of the present invention is made further surer.
Furthermore, in addition to the first and second aspects of the present invention, a third aspect of the present invention is characterized in that a difference between a resonance frequency of the ultrasonic oscillator and an anti-resonance frequency thereof is regulated to be 1 kHz or more.
In addition to the effects of the first and second aspects of the present invention, according to the third aspect of the present invention, since the difference between the resonance frequency of the ultrasonic oscillator and the anti-resonance frequency close to the resonance frequency is regulated to 1 kHz or more, stable oscillation with high efficiency can be achieved even when the load change occurs, in addition to the effects of the first and second aspects. When the plurality of resonance frequencies exist, the resonance frequency means a frequency at which impedance of the oscillator is the lowest, and the anti-resonance frequency is a frequency close to the resonance frequency, at which the impedance of the oscillator shows a high peak. Accordingly, an excellent cleaning effect can be exhibited with less power, and dirty clothes can be cleaned easily.
Noted that the resonance frequency means a frequency at which the oscillation is the largest and the impedance of the oscillator is low, and the anti-resonance frequency is a frequency at which the impedance of the oscillator is high.